1. Technical Field
The invention relates to a method and apparatus for handling of calls for emergency services in telecommunications networks and, in particular, to routing within an intelligent network of emergency services calls from mobile stations.
2. Background Art
In existing telecommunications networks, particularly in North America, telephone calls for emergency services are routed to a Public Service Access Point (PSAP) which is staffed by emergency services operators and, for reasons of reliability and continuity of service, is accessed by way of a tandem switch dedicated to such emergency services. To access emergency services, the caller dials the emergency services access code, which in North America is 9-1-1. When the end office detects the digits 9-1-1, instead of routing the call like a normal voice call, it routes the call immediately to the 9-1-1 tandem switch which routes the call to the Public Service Access Point. In order to determine the most appropriate emergency services centre to provide the required services, the emergency services operator will determine the location of the caller by first obtaining the calling line identifier, either automatically if the tandem switch is provisioned with Automatic Number Identification (ANI), or by questioning the caller, and using it to access an Automatic Location Identification database and obtain the geographical location of the caller.
Although it is usual to provide a second ALI database as a xe2x80x9chot sparexe2x80x9d to ensure reliability of service, this existing way of handling emergency services calls is not entirely satisfactory because, if the trunks between the end office and the dedicated tandem switch, or between the tandem switch and the PSAP, were blocked, that PSAP could not supply the necessary emergency service to that caller. A further disadvantage is that automatic location identification is not available for mobile users.
An object of the present invention is to overcome or at least mitigate these deficiencies of existing emergency services systems. To this end, the present invention provides for calls for emergency services to be alternate routed using out-of-band or common channel signalling.
According to one aspect of the present invention, there is provided a telecommunications network comprising an intelligent network portion comprising a Service Control Point (SCP), a plurality of Service Switching Points (SSP), one or more Public Service Access Points (PSAP) and a Signal Mediation Point (SMP), and a mobile network portion comprising a Mobile Services Switching Centre (MSC) for routing calls from mobile users in cell sites associated with such MSC and a Home Location Register (HLR), the MSC and SSPs being interconnected by trunks for routing calls therebetween, the MSC and SSPs being connected to the SMP by Signalling System No. 7 (SS7) signalling links, the SMP being connected to the SCP and the HLR by respective SS7 links, the SCP having access to a routing table including entries correlating routing numbers of PSAPs with cell site identifiers, the SMP having basic SCP SS7 applications part software for handling mobile or wireline TCAP messages and additional conversion software and tables for translating TCAP message parameters according to mobile protocols to TCAP message parameters using intelligent network protocols, and vice versa, the method comprising the steps of: at the MSC:
upon receipt of a 9-1-1 call from a mobile station, forming a TCAP query message addressed to the destination point code of the HLR and routing the message to the SMP, the message including a mobile identification number (MIN) for the mobile station, a cell site number, and a mobile network address for the MSC, and the dialled digits, at the SMP:
detecting the dialled digits identifying the call as an emergency services call;
translating the parameters in the message as received into corresponding AIN/IN parameters according to the intelligent network protocol being used by the SCP,
forming an AIN/IN TCAP message including the translated parameters, the network address of the MSC and the cell site number being combined in an Original Calling Party number,
overriding the destination point code of the HLR and routing the message instead to the SCP, at the SCP,
accessing the mobile routing table using the Original Calling Party number from the received query and obtaining a routing number for a PSAP,
including the PSAP network address in a TCAP response message and sending this response message to the SMP, at the SMP,
translating the intelligent network parameters of the TCAP response message into corresponding mobile network parameters,
and routing the response message to the MSC, at the MSC,
extracting the PSAP network address from the TCAP message and routing the emergency services call thereto via one or more of the SSPs.
According to a second aspect of the invention, there is provided Signal Mediation Point apparatus comprising SCP software for processing and routing TCAP messages and conversion software for translating parameters of such TCAP messages formulated according to one or more mobile protocols into parameters according to one or more intelligent network protocols, and vice versa, the SMP having signalling links for connection to a Mobile Switching Centre, a Service Control Point and a Home Location Register, the conversion software being operative, upon receipt of a query from the MSC containing a destination point code for the HLR and dialled digits of an emergency services call to detect said digits, translate the parameters into corresponding intelligent network parameters, change the destination point code to that of the SCP, and route the message to the SCP, and on receipt of a response from the SCP, to detect the emergency services dialled digits again, translate the parameters into corresponding mobile network parameters, and route the response message to the MSC.
The conversion software may determine a network address of the mobile switching centre and a cell site identifier and combine both into an Original Calling Party number in the intelligent network TCAP message sent to the SCP.
Various objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description, taken in conjunction with the accompanying drawings, of preferred embodiments of the invention, which are described by way of example only.